Different Types of Culture Media
To grow microorganisms the medium provide:
a) All essential nutrients
b) Ions e.g. K+, Na etc.
d) Correct pH
e) Osmotic pressure
Should also neutralize all produced toxic materials
Should be incubated in correct temperature in the right atmosphere and for adequate period of time.
Main Types of Media
1) Basic media examples nutrient agar (solid), nutrient , broth (Fluid):
They support all organisms without special requirement
They are usually used for preparation of enriched media
To maintain stock culture
To sub-culture pathogens from differential or selective media
To do susceptibility testing
2) Enriched example blood agar or chocolate agar produced by adding whole blood or serum or yeast extract to basic media to grow organisms needing special requirements e.g. H.influenzae, _________.
3) Enrichment Media:
Selective fluid media which contain substance that inhibit the growth of unwanted organisms e.g. those for isolation of Salmonella from faeces.
4) Selective: e.g. MacConkey or XLD or DCA solid media containing chemicals, bile salts dyes or antibiotic which suppress unwanted organisms. Usually used in culturing specimens from body sites with normal flora e.g. stools, urine and sputum.
5) Indicator or differential media contain dyes or other substance to differentiate organism could be enriched (blood agar0 or selective (MacConkey).
6) Transport media:
CARY – Blair medium
They are usually semisolid media contain substances which suppress commensal organisms:
Used for transport of specimen if cannot be culture soon.
7) Identification media:
Media to which substrates or chemicals are added to help identify organism e.g. peptone water sugars Kligler iron agar
8) Solid, semisolid and fluid media:
Solid media re made by adding agar (a polysaccharide substance) at concentration of 1.5% (Agar mello at (90-95oC) settles at (32-39oC)
Solid media help to show Bacterial colony morphology
Semisolid agar 0.4 -0.5% used to help to show bacterial motility also for transport media
Fluid media increase the number of bacteria, also for identification
Selection of Culture Media
It depends on
a) Pathogens to be isolated, their growth requirement, and their characteristic features.
b) Origin of specimen with or without normal flora
c) Cost, availability
d) Training and experience of the laboratory staff.
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